Sampling clocks of a transmitter and a receiver in a communication system may not be fully synchronized, for obtaining a sending signal at the receiving end correctly, the problem of the non-synchronization between the clock of the transmitter and the clock of the receiver needs to be solved, and clock recovery is exactly used to address the problem of the non-synchronization of the sampling clocks of the transmitter and receiver.
Coherent digital receivers are commonly used in modern communication digital receivers, and the coherent digital receiver can compensate for transmission impairments of a received signal in a digital domain, such as chromatic dispersion compensation, polarization mode dispersion compensation, clock recovery, frequency offset compensation, and phase compensation, etc. A clock recovery module may extract a sampling clock frequency and a sampling phase from a sampled digital signal correctly, and compensate the signal for an error, so as to demodulate a transmitting signal correctly.